Yamaha TRX850 Enthusiasts Forum

Does anyone know off hand what a TRX 850 piston weighs in grams?

Going to be stripping the engine this year to overhaul gearbox and i

had thought while i was doing that maybe i could add a pair of ceramic coated pistons.

Crank balancing is essential so i would like to be 1-2 grams within limit of primary.

No need for secondary 270 crank sorts that.

Alastair wrote:Does anyone know off hand what a TRX 850 piston weighs in grams?

Going to be stripping the engine this year to overhaul gearbox and i

had thought while i was doing that maybe i could add a pair of ceramic coated pistons.

Crank balancing is essential so i would like to be 1-2 grams within limit of primary.

No need for secondary 270 crank sorts that.

Still have secondaries Alistair - the rods aren't on a common crankpin so you'll get rocking couples. The balancer shafts help that though. There's still the non-sinusoidal piston motion to deal with - which exists in all engines - especially long strokers.

A friend of mine took his 900 TDM out to 960 using pistons balanced to as close as the standard ones but it does buzz more than mine even though we both have carrillo rods fitted

TRX850 stock


TDM900 stock (new)


Custom 907cc (designed for a TRX wrist / gudgeon pin, TDM is different so are NOT compatible).


Custom JE pistons. And ill bet a fair bit of money you wont be able to get em They are not listed, are total custom and not for reproduction. They are also 12.5:1 up from 10.5:1 comp.. woot.

Did YOU commission them Quan-Time,I`m guessing crankcase mouth modifications are required,along with rods?
And what about the cylinder head too?

After Australia day celebrations the Barman said to me YOUR Pissed n Wait till ya sober up till ya next beer...A beers only 285ounces up here in QLD

my mistake 7 ounces 285ml

yer. Some mods are required to accomodate them.. You wouldnt be able to use them in a normal bored out block. I had to punch out my old sleeves, bore out the block, make new sleeves and press them in, and then hone to size. Where the block mates with the top case, some relief work also needs to be done.
Cyl head work is not hugely required, BUT obviously recommended to access the full potential.
Considering i own a flowbench, its not a huge hurdle for me.

Ive been thinkin of doing a "stock" port job and digitising it and offering a CNC exchange program. But thats really on the back burner. The head port that im half way thru is a bit.. "different". When its done ill post pics and flow numbers.
And im making custom throttle bodies too